Immunological techniques combined with formal genetic analysis of mutations will be used to analyze the genetic regulatory network controlling expression of stage-specific cuticle antigens of the nematode Caenorhabditis elegans. Stage-specific surface antigens will serve as developmental markers to identify, by mutation, genes controlling post-embryonic stage transitions. Immunofluorescence, cell lineage studies, and monoclonal antibody reagents will be used to study stage-specific phenotypes of mutants with alterations in timing of surface antigen expression. Genes will be mapped and assigned to complementation groups using the surface antigen phenotype as marker. Preliminary molecular genetic analysis of genes involved in surface antigen expression will be undertaken by analyzing "transposon-tagged" genes and by selecting surface antigen coding DNA sequences from expression-linked genomic DNA libraries, using anti-cuticle antibodies as probes. How genes specify animal development and differentiation is a major unsolved problem in biology. If the proposed study is successful, regulatory genes controlling the timing of events in the life of a multi-cellular animal would be identified and therefore become available for study. Such major regulatory genes may also control development, both normal and abnormal, in humans.